It is well established that the detection of a luminance-defined Gabor is improved if measured in the presence of two high contrast aligned flanking Gabors (Polat and Sagi, Vis. Res., 1993) and this is termed flank facilitation. Here we investigate whether this facilitation occurs for isoluminant chromatic stimuli. We measured the effect of flank facilitation for achromatic and chromatic Gabors, (0.75 cpd, 1 octave bandwidth). Stimuli isolated either the S-cone opponent mechanism, the L/M cone opponent mechanism, or the achromatic mechanism. We used a 2AFC paradigm with a double staircase to measure, in a blocked design, the detection threshold of a central Gabor target presented alone and in the presence of two flanking Gabors. Three conditions were investigated: 1) target and flanks all of the same color and spatial phase, 2) target and flanks of the same color but different phase (180 degrees), 3) target and flanks of different colors. Results were collected for 3 different target-flank distances (2, 3, 6 ?) in three subjects. A facilitation effect occurred when the target and flanks were the same color and same phase and its magnitude decreased as the target-flank distance increased., There was no facilitation in the out of phase conditions for achromatic or chromatic stimuli. A weaker and inconsistent facilitation effect was found in crossed (i.e. achromatic/chromatic) conditions. A comparable degree of flank facilitation occurs in both achromatic and chromatic mechanisms that exhibits phase dependence. There is no consistent cross interaction between color and luminance mechanisms.